Method of manufacturing secondary aromatic amines



Patented Nov. 6, 1934 UNITED STATES METHOD OF MANUFACTURING SECONDARY AROMATIC AMINES Waldo L. Semon, Cuyahoga Falls, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application February 15, 1929,

Serial No. 340,339

15 Claims.

This invention relates to anti-oxidants for rubber, and to the process of making the same, particularly to improved anti-oxidants of the secondary aromatic amine type and the process by 5 which they are prepared.

It is well known that rubber normally deterio- "rates when exposed to light, heat or air, its tensile strength, resiliency and other desirable properties suffering as a consequence. Heretofore numerous -age-resisters or anti-oxidants such as aldehyde-amine derivatives and secondary aromatic amines have been proposed and used considerable success in retarding such deterioration.

.15 This invention, in brief, comprises making an improved anti-oxidant for rubber or similar materials by reacting an amino-substituted phenol with an aromatic amine in the presence of a catalyst. In its preferred form, the method of this invention comprises heating the hydrochloride of an amino-phenol with the hydrochloride of an aromatic amine, the hydrogen chloride acting as p "a. catalyst and promoting the condensation of the molecules with the elimination of ammonia or water, but substantially the same product is obtained if the bases are mixed and hydrochloric aoid,*or even another strong acid such as hydrobromic acid, added thereto. Under certain conditions thereaction may also be carried out in the 3o presenceof iodine or other catalyst, or in solution,

but in-general the procedure is simplerif the two reacting materials are heated together in the presence of substantial proportionseof hydrochloric acid.

The process of this invention will be described .aminophenol salt, and the mixture is heated under 2, reflux condenser for 2 to 10 hours at a temperature of about 250 C. The product is poured into water. The insoluble precipitate is separated and washed. This materialmay be resinous or crystalline, depending upon'condi- -PATENT OFFICE tions, and is an excellent anti-oxidant in rubber.

The reactions taking place are rather complex, but the two following equations are typical of what occurs during the reaction:

aniline hydrochloride p-aminophenol hydrochloride p-hydroxy-diphenylamine mums hydrochloride p-hydoxy diphenylamine symmetrical diphenyl-p-phenylene-diamine Other similar reactions take place among the aniline and the p-aminophenol, and the inter- Among the products of the mediate products. reaction are found:

diphenylamine,

I p-hydroxy-diphenylamine, III w p,p-dihydroxy-diphcnylamine,

' symmetrical diphenyl p-phenylene diamine, and

p-hydroxy diphenyl p-phenylene diamine,

as well as other compounds of similar constitution, but with a more complex molecule.

The complex mixture of products formed by the reaction of p-aminophenol hydrochloride and aniline hydrochloride is very dii'ficult to separate into its individual constituents, but the separation is neither necessary nor desirable, inasmuch as the constituent products are each and all excellent anti-oxidants and the mixture presents certain advantages over the pure substance from the point of view of activity, solubility in rubber, etc. I r

The process of this inventionmayw be carried out with widely different proportionsof the. reacting materials. However, it is preferred to react one molecular equivalent of .the aminophenol with from one-half to five molecular equivalents of the aniline or other aromatic amine. A change in the proportions results in the'formation of difierentproportions of the various products described above. Since these products are all extremely active age-resisters,

it is ordinarily: of little importance which one or ones predominate." For example, if p-aminophenol is present in excess, a comparatively large proportion of hydroxy-substituted secondary amines is formed, while if aniline is present in larger amounts the diphenylamine, and especially the diphenyl-p-phenylene diamine, tends to predominate. Thus, if one molecular equivalent of'p-aminophenol hydrochloride is heated with four or more molecular equivalents of aniline hydrochloride, a good yield of. diphenyl p-phenylene diamine is obtained. The pure material maybe isolated by neutralizing and steam distilling the unreacted excess aniline and crystallizingthe residual portion of the product from a convenient solvent, such as toluene.

To illustrate'the exceedingly small effect produced by a change in the proportions of the reacting materials, one .molecular equivalent of p-aminophenol hydrochloride was heated respec-' tively with twoand with four molecular equivalents of aniline hydrochloride, theproducts being termed A and B.

A typical tireitread composition was prepared containing: blended plantation rubbers 100 parts "by weight, sulphur 5.5 parts, zincoxide 30 parts,

for minutes at 145 C. (294 F.) to produce an.

optimum cure. The relative rates of aging of the vulcanized compositions were compared by measuring their respective tensile strengths and elongations before and after aging-Accelerated aging tests were carried out in the Geer aging oven, in which samples were maintained at a temperature of C. (158 F.) in a constantly renewed stream of air, as Well as in the Bierer-Davis bomb, in'

which other samples were maintained at the same temperature (70 C.) in an atmosphere of oxygen at a pressure of 300 lbs. per sq. in. --In the table below T indicates .ultimate tensile strength in lbs. per sq. in. and E indicates ultimate elongation in per cent. of original length.

Accelerated aging tests It is evident thatthe two anti-oxidants A and B are extremely effective in retarding the deterioration of rubber, and that they possess substantially the same activity.

Very similar products with equally good antioxidant properties may be obtained by reacting a homologue of p-aminophenol such as 5-aminocresol-2, etc. with a primary aromatic amine. Likewise, other primary aromatic amines, such as the vtoluidines, the xylidenes, aminobiphenyl, naphthylamine, etc., may be substituted for the aniline. I

While I have herein disclosed certain preferred manners of performing my invention, I do not thereby desire orintend to, limit myself solely thereto, for, as hitherto stated, the precise pro-.- portions of the materials utilized may be varied and other materials having equivalent chemical properties may be employed if desiredwithout departing from the spirit and scope of the invention as defined in the appendedclaims.

Iclaim:

1. The method of making an anti-oxidantconsisting of a mixture of secondary aromatic amines which comprises reacting an unsubstituted .primary arylamine with a substance selected from the class consisting of p;-aminophenol and its homologuesunder substantially anhydrous conditions in the, presence of a catalyst selected from the class consisting of hydrohalic acids 1 iodine. i

2. The method of making an anti-oxidant consisting of a mixture of secondary aromatic amines which comprises reacting'anunsubstituted primary arylamine with a substance selected from the class consisting of p-aminophenol and its homologues under substantially anhydrous con-- ditions in the presence of hydrochloric acid. v

3. The method of making an anti-oxidant consisting of a mixture of secondary aromaticamines which comprises heating thehydrochlorideof an unsubstituted primary arylamine with p-aminophenol hydrochloride under substantially anhydrous conditions. .7 I g 4. The method of I making an anti-oxidant consisting of a mixture of secondary aromatic amines which comprises heating -p-aminophenol hydrochloride with the hydrochloride of a base selected from the'class consisting of aniline and its homologues. j

5. The method of making ananti-oxidant consisting of a mixture of, s'econdaryaromaticamines which comprises heating p-aminophenol hydrochloride with aniline hydrochloride. v

6. .The method of vmaking an anti-oxidant corrsisting of a mixture of secondary aromatic amines which comprises heating one molecular equivalent of p-aminophenol hydrochloride with from one-half to five molecular equivalents of aniline hydrochloride. 7

'7. The method of making an anti-oxidant consisting of a mixture of secondary aromatic amines which comprises heating a mixture of one molecular equivalent of p-aminophenol hydrochloride and from one-half to five molecular equivalents of aniline hydrochloride to a temperature of from 200 to 300 C.

8. The method of making symmetrical diphenyl p-phenylene diamine which comprises heating one molecular equivalent of p-amino phenol hydrochloride with at least four molecular equivalents of aniline hydrochloride.

9. The method of making symmetrical diphenyl p-phenylene diamine which comprises heating one molecular equivalent of p-aminophenol with at least four molecular equivalents of aniline hydrochloride, neutralizing and steam distilling the unreacted materials, and separating the diphenyl p-phenylene diamine from the residual product by crystallization from solution.

10. An anti-oxidant consisting of a mixture of secondary aromatic amines resulting from the reaction of an unsubstituted primary arylamine with a substance selected from the class consisting of p-aminophenol and its homologues under such conditions that both water and ammonia are eliminated.

11. An anti-oxidant consisting of a mixture of secondary aromatic amines resulting from the reaction of an unsubstituted primary arylamine with a substance selected from the class consisting of p-aminophenol and its homologues in the presence of a catalyst selected from the class consisting of hydrohalic acids and iodine.

12. An anti-oxidant consisting of a mixture of secondary aromatic amines resulting from the reaction of an unsubstituted primary arylamine with a substance selected from the class consisting of p-aminophenol and its homologues in the presence of hydrochloric acid with the elimina- WALDO L. SEMON. 

